The invention relates to a polyarylene sulfide resin composition and an optical instrument part therefrom.
Recently, a thermoplastic resin having a high resistance to heat and chemicals is desired for a material for electric or electronic parts, automobile parts or chemical apparatus parts. Polyarylene sulfide (hereinafter, abbreviated as PAS), e.g., polyphenylene sulfide (hereinafter, abbreviated as PPS), attracts attention in recent years, to meet this requirement. However, PAS has a drawback that it tends to evolve corrosive gas such as HCl, SO2, H2S, at a high temperature, particularly in a molten state in an oxygen atmosphere, so that it causes to rust a mold and insert part adjoining to PAS. Another drawback is that a lot of gum adheres to an injection mold.
To solve the drawback regarding the corrosive gas, many methods have been proposed. For example, Japanese Patent Application (JPA) Laid-Open S59-209644 and JPA Laid-Open S60-1241 disclose a method where an inorganic gas scavenger is added to PAS. JPA Laid-Open S60-115658 discloses a method where a corrosive acidic gas evolving from PAS is neutralized by adding a low molecular weight polyamine compound to PAS.
However, the corrosive acidic gas cannot be removed sufficiently by these methods and, accordingly, the formation of rusts caused by the corrosive gas evolving from PAS cannot be prevented for a long time. Further, short-term quick corrosion as well as long-term corrosion of metal adjoining to PAS cannot be solved.
To solve the problem, JPA Laid-Open H6-322271 discloses a PAS resin composition characterized in that it comprises 100 parts by weight of PAS, 0.5 to 10 parts by weight of at least one inorganic filler selected from the group consisting of hydrotalcite compounds and Mg/Al oxides solid solutions, and 0.05 to 3 parts by weight of di(cyclohexyl)ammonium nitrite. However, the composition is still insufficient to reduce corrosive gas and prevent the generation of gum.
JPA Laid-Open S62-167355 describes a method where sodium aluminate is added to PAS to thereby reduce the corrosive gas. However, the generation of the gum cannot be prevented sufficiently by the method.
It is known to use PAS for optical parts such as an object lens driving unit. In JPA Laid-Open H10-143891, a composition of PPS and 20 to 60% of PTFE is used to improve hysteresis and to enhance dimensional precision of a bearing for an object lens driving unit. JPA Laid-Open S62-223822 describes a monolithic PPS lens-holding plate and a monolithic PPS bearing part for a lens holder of an object lens driving unit. The aforesaid plate and part molded from PPS do not have a satisfactory dimensional precision and discoloration caused by gas yellowing is not prevented sufficiently.
The purpose of the present invention is to provide a polyarylene sulfide resin composition which evolves a significantly reduced amount of the corrosive gas at a high temperature, particularly in a molten state in an oxygen atmosphere whereby discoloration due to gas yellowing is little, and further, the amount of gum evolved from the composition is also small, and still further the dimensional precision is extremely good, that is a dimensional reproducibility in a repetitive molding is excellent. Thus, the present composition is particularly suited to be used for an optical instrument part such as an object lens driving unit.
The present invention is (1) a resin composition comprising 100 parts by weight of (A)polyarylene sulfide, and 0.01 to 5.0 parts by weight of (B) a product compound of an element selected from the group consisting of group IIA and group IIB of the periodic table, wherein said product compound has such alkalinity that a mixture of said product compound with a 20-fold weight of ultrapure water of grade A4 specified in the Japanese Industrial Standards (JIS) K0557 has a pH of from 10.0 to 12.0.
Preferred embodiments of the present invention are as follows.
(2) The composition described in (1) above, wherein the product compound (B) has a BET specific surface area of 10 m2/g or larger.
(3) The composition described in (1) above, wherein the product compound (B) has a BET specific surface area of 14 m2/g or larger.
(4) The composition described in (1) above, wherein the product compound (B) has a BET specific surface area of 20 m2/g or larger.
(5) The composition described in any one of from (1) to (4) above, wherein the product compound (B) is contained in an amount of from 0.05 to 4.0 parts by weight.
(6) The composition described in anyone of from (1) to (5) above, wherein the product compound (B) has the pH of from 10.5 to 11.5.
(7) The composition described in any one of from (1) to (6) above, wherein the product compound (B) is a magnesium compound or a zinc compound.
(8) The composition described in (7) above , wherein the magnesium compound is at least one selected from the group consisting of magnesium oxide, magnesium hydroxide and magnesium silicate.
(9) The composition described in (7) above wherein the zinc compound is at least one selected from the group consisting of basic zinc acetate, zinc phosphate, zinc acetate, and basic zinc chloride.
(10) The composition described in any one of from (1) to (9) above, wherein (C) an inorganic filler is further comprised in an amount of from 0 to 250 parts by weight.
(11) The composition described in any one of from (1) to (9) above, wherein (C)an inorganic filler is further comprised in an amount of from 0 to 200 parts by weight.
(12) A part of an optical instrument, made of the resin composition described in any one of from (1) to (11) above.
(13) A part of an object lens driving unit, made of the resin composition described in any one of from (1) to (11) above.
(14) The part of an object lens driving unit described in (13) above, wherein the part is a lens holder, a holding vessel, or a housing body.